1. Field of the Invention
The present invention relates to an electric fan adapted for forcibly cooling a radiator by energizing a fan motor when the temperature of engine cooling water is elevated, and more particularly it pertains to an automotive electric fan controlling device which is so designed as to interrupt the energization of the fan motor when the speed of air flow through the radiator when the motor vehicle is running, becomes higher than a predetermined speed, thereby minimizing consumption of battery power.
2. Description of the Prior Art
In order to have a better understanding of the present invention, reference will first be made to FIG. 1 which illustrates a conventional device for controlling an electric fan adapted for cooling a radiator. In the illustrated conventional device, a fan motor 5 for the electric fan 4 is supplied with electric power from a battery through an ignition switch 1 and a thermo-switch 3 which is turned on when the temperature of engine cooling water passed to the radiator 2 is higher than a predetermined value. More specifically, in case the engine cooling water temperature becomes higher than the predetermined value, the thermo-switch 3 is turned on so that the fan motor 5 is energized to cause the electric fan 4 to be rotated, whereby the radiator 2 is forcibly cooled and thus the engine cooling water temperature is prevented from being elevated.
Such a conventional device for forcibly cooling the radiator by means of the electric fan is suitably employed with a front-engine, front drive (FF) type motor vehicle, and is able to positively avoid overheating of the engine by virtue of the face that the electric fan 4 is rotated only when the engine cooling water temperature becomes higher than the aforementioned predetermined value.
Since the speed of rotation of the electric fan 4 effected by the fan motor 5 is substantially constant, the speed (shown at A in FIG. 2) of air flow produced at the front face of the radiator when the motor vehicle is running with the electric fan 4 being stopped, becomes substantially equal to the speed (shown at B in FIG. 2) of air flow produced at the front face of the radiator when the motor vehicle is running with the electric fan 4 being rotated, in the case where the running speed of the motor vehicle is increased to a certain extent.
Thus, when the running speed of the motor vehicle is higher than a predetermined speed, the speed of air flow introduced into the radiator 2 due to the motor vehicle running is higher than the speed of air flow sucked in through the radiator due to the rotation of the electric fan effected by the fan motor 5 which is energized upon closure of the thermo-switch 3. This means that the cooling effect produced by passing cooling air through the radiator 2 by means of the electric fan 4 is less in such a case; in other words, even if the electric fan 4 is stopped, cooling effect for the radiator 2 substantially equivalent to that produced when the electric fan 4 is rotated, can be achieved by the air flow produced due to the motor vehicle running. As mentioned above, in the foregoing conventional device, the electric fan 4, which consumes a relatively large proportion of battery power, is continuously driven irrespective of the running speed of the motor vehicle; thus the conventional device is disadvantageous in that battery power is wastefully consumed.